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Bridge/Router. By: Zach Sylte. How Routers work:.

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bridge router


By: Zach Sylte


How Routers work:

  • A router is a computer networking device that forwards data packets toward their destinations through a process known as routing. Routing occurs at layer 3 of the OSI seven-layer model. Routing is most commonly associated with the Internet Protocol, although other less-popular routed protocols remain in use.

How Routers work:

  • Much of the work to get a message from one computer to another is done by routers, because they're the crucial devices that let messages flow between networks, rather than within networks.
  • The router is the only device that sees every message sent by any computer

How Routers work:

  • One of the tools a router uses to decide where a packet should go is a configuration table.
  • A configuration table is a collection of information, including:
    • Information on which connections lead to particular groups of addresses
    • Priorities for connections to be used
    • Rules for handling both routine and special cases of traffic
  • A configuration table can be as simple as a half-dozen lines in the smallest routers, but can grow to massive size and complexity in the very large routers that handle the bulk of Internet messages.

How Routers work:

  • A router, then, has two separate but related jobs:
    • The router ensures that information doesn't go where it's not needed. This is crucial for keeping large volumes of data from clogging the connections of "innocent bystanders."
    • The router makes sure that information does make it to the intended destination.
  • It joins the two networks, passing information from one to the other and, in some cases, performing translations of various protocols between the two networks.
  • It also protects the networks from one another, preventing the traffic on one from unnecessarily spilling over to the other.

How Routers work:

  • Internet data, whether in the form of a Web page, a downloaded file or an e-mail message, travels over a system known as a packet-switching network.
  • In this system, the data in a message or file is broken up into packages about 1,500 bytes long. Each of these packages gets a wrapper that includes information on the sender's address, the receiver's address, the package's place in the entire message, and how the receiving computer can be sure that the package arrived intact.
  • Each data package, called a packet, is then sent off to its destination via the best available route -- a route that might be taken by all the other packets in the message or by none of the other packets in the message.

How Routers work:

  • This might seem very complicated compared to the circuit approach used by the telephone system, but in a network designed for data there are two huge advantages to the packet-switching plan.
    • The network can balance the load across various pieces of equipment on a millisecond-by-millisecond basis.
    • If there is a problem with one piece of equipment in the network while a message is being transferred, packets can be routed around the problem, ensuring the delivery of the entire message.

How Routers work:

  • Packet-switching Network- is an interconnected set of networks that are joined by routers or switching routers. The most common packet-switching technology is TCP/IP, and the Internet is the largest packet-switched network.
  • Packet- is a unit of data that is transmitted across a packet-switched network.
  • Router- This is a hardware device that routes data from a local area network (LAN) to another network connection.
  • Protocols- a set of rules governing the format of messages that are exchanged between computers.

How Routers work:

  • The routers that make up the main part of the Internet can reconfigure the paths that packets take because they look at the information surrounding the data packet, and they tell each other about line conditions, such as delays in receiving and sending data and traffic on various pieces of the network.
  • Not all routers do so many jobs, however.

The Path of a Packet:


How Routers work:

  • Routers are one of several types of devices that make up the "plumbing" of a computer network. Hubs, switches and routers all take signals from computers or networks and pass them along to other computers and networks
  • But a router is the only one of these devices that examines each bundle of data as it passes and makes a decision about exactly where it should go. To make these decisions, routers must first know about two kinds of information: addresses and network structure.
  • There is the Logical address and the Physical address

How Routers work:

  • Logical Address-It describes a way someone can get a message to you.
  • Physical Address or MAC Address-You generally only see when you're buying or selling a piece of property.

How Routers work:

Logical Address:

  • The logical address is what the network uses to pass information along to your computer.
  • Your computer can have several logical addresses at the same time. Of course, you're used to having several "logical addresses" bring messages to one physical address. Your mailing address, telephone number and e-mail address all work to bring messages to you when you're in your house.
  • Logical addresses for computer networks work in exactly the same way. You may be using the addressing schemes, or protocols, from several different types of networks simultaneously

How Routers work:

  • The chances are very good that you'll never see the MAC address for any of your equipment because the software that helps your computer communicate with a network takes care of matching the MAC address to a logical address.

MAC Address:


How Routers work:

Understanding the Protocols

  • The first and most basic job of the router is to know where to send information addressed to your computer.
  • Routers are programmed to understand the most common network protocols. That means they know the format of the addresses, how many bytes are in the basic package of data sent out over the network, and how to make sure all the packages reach their destination and get reassembled.
  • Moving the package along to its destination isn't all that a router will do. It's just as important, in today's computerized world, that they keep the message flowing by the best possible route.


  • In April 1967, a computer scientist by the name of Wesley A. Clark suggested the idea to incorporate IMP Interface Message Processor  to the ARPANET (Advanced Research Projects Agency Network) during a design session with Lawrence Roberts, chief scientist of ARPANET.


Net Gear

D Link





Air Link

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  • Linksys E1000- $69.99
  • Linksys E2000- $99.99
  • Linksys E3000- $179.99

how the router knows which computer is correct
How the router knows which computer is correct
  • The router examines the bundle of data and makes the decision as to where it should go.
  • To make the decision the router must know: The address and network structure


  • Is a device that separates two or more network segments within one logical network
  • A bridge is usually placed between two separate groups of computers that talk with each other, but not that much with the computers in the other group.


  • A good example of this is to consider a cluster of Macintoshes and a cluster of Unix machines. Both of these groups of machines tend to be quite chatty amongst themselves, and the traffic they produce on the network causes collisions for the other machines who are trying to speak to one another.